ELECTRICAL GURU

Important questions in EE 1. What is a System? When a number of elements or components are connected in a sequence to perform a specific function, the group of elements that all constitute a System 2. What is Control System? In a System the output and inputs are interrelated in such a manner that the output quantity or variable is controlled by input quantity, then such a system is called Control System. The output quantity is called controlled variable or response and the input quantity is called command signal or excitation. 3. What are different types of Control Systems? Two major types of Control Systems are 1) Open loop Control System 2) Closed Loop Control Systems Open loop Control Systems:The Open loop Control System is one in which the Output Quantity has no effect on the Input Quantity. No feedback is present from the output quantity to the input quantity for correction. Closed Loop Control System:The Closed loop Control System is one in which the feedback is provided from the Output quantity to the input quantity for the correction so as to maintain the desired output of the system. 4. What is a feedback in Control System? The Feedback in Control System in one in which the output is sampled and proportional signal is fed back to the input for automatic correction of the error ( any change in desired output) for futher processing to get back the desired output. 5. Why Negative Feedback is preffered in the Control System? The role of Feedback in control system is to take the sampled output back to the input and compare output signal with input signal for error ( deviation from the desired result).  Negative Feedback results in the better stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations. Hence in control systems negative feedback is considered.   6. What is the effect of positive feedback on stability of the system? Positive feedback is not used generally in the control system because it increases the error signal and drives the system to instability. But positive feedbacks are used in minor loop control systems to amplify certain internal signals and parameters 7. What is Latching current? Gate signal is to be applied to the thyristor to trigger the thyristor ON in safe mode. When the thyristor starts conducting the forward current above the minimum value, called Latching current, the gate signal which is applied to trigger the device in no longer require to keep the scr in ON position. 8. What is Holding current ? When scr is conducting current in forward conduction state, scr will return to forward blocking state when the anode current or forward current falls below a low level called Holding current Note: Latching current and Holding current are not same. Latching current is associated with the turn on process of the scr whereas holding current is associated with the turn off process. In general holding current will be slightly lesser than the latching current. 9. Why thyristor is considered as Charge controlled device? During the triggering process of the thyristor from forward blocking state to forward conduction state through the gate signal, by applying the gate signal (voltage between gate and cathode) increases the minority carrier density in the p-layer and thereby facilitate the reverse break over of the junction J2 and thyristor starts conducting. Higher the magnitude of the gate current pulse, lesser is the time required to inject the charge and turning on the scr. By controlling the amount of charge we can control the turning on time of the scr. https://t.me/ElectricalGuru

21)   Slip ring induction motor has  a. Low starting torque b. Medium starting torque c. High starting torque d. None of these ANSWER: High starting torque 22)   The frequency of rotor current in an induction motor is  a. slip times the frequency of stator current b. slip times the frequency of supply c. One by slip times the frequency of stator current d. One by slip times the frequency of supply ANSWER: slip times the frequency of supply 23)   Slip of an induction motor increases with  a. increase in current and decrease in torque b. increase in current and torque c. decrease in current and torque d. decrease in current and increase in torque ANSWER: increase in current and torque 24)   In an induction motor, rotor speed is always  a. Less than the stator speed b. More than the stator speed c. Equal to the stator speed d. None of these ANSWER: Less than the stator speed 25)   The frequency of the induced emf in an induction motor is  a. Greater than the supply frequency b. Lesser than the supply frequency c. Same as the supply frequency d. None of these ANSWER: Same as the supply frequency 26)   The efficiency of the transformer will be maximum when  a. Iron losses is equal to the twice of the copper losses b. Copper losses is equal to the twice of the iron losses c. Iron losses is equal to the copper losses d. All of these ANSWER: Iron losses is equal to the copper losses 27)   Copper losses is proportional to  a. kVA b. square of kVA c. cube of kVA d. none of these ANSWER: square of kVA 28)   If the transformer is loaded then the secondary terminal voltage falls for and rises for  a. Lagging power factor, leading power factor b. Lagging power factor, unity power factor c. Unity power factor, lagging power factor d. Leading power factor, lagging power factor ANSWER: Lagging power factor, leading power factor 29)   Efficiency of a transformer is maximum at  a. Leading power factor b. Lagging power factor c. Unity power factor d. None of these ANSWER: Unity power factor 30)   Copper losses occurs due to ohmic resistance in  a. Primary winding b. Secondary winding c. Both primary and secondary winding d. None of these ANSWER: Both primary and secondary winding https://t.me/ElectricalGuru

Lithium cells operates ranging from  a. -25 ° C to 25 ° C b. -50 ° C to 25 ° C c. -50 ° C to 75 ° C d. -75 ° C to 75 ° C ANSWER: -50 ° C to 75 ° C 12)   The positive plates of nickel iron cell is made up of  a. Nickel hydroxide b. Lead peroxide c. Ferrous hydroxide d. Potassium hydroxide ANSWER: Nickel hydroxide 13)   In lead acid accumulators, the container is filled with distilled water and concentrated sulphuric acid in the ratio of  a. 1 : 2 b. 2 : 1 c. 3 : 1 d. 1 : 3 ANSWER: 3 : 1 14)   The emf of the dry cell is about  a. 0 V b. 0.5 V c. 1 V d. 1.5 V ANSWER: 1.5 V 15)   In leclanche cell, anode is packed in a porous pot containing  a. manganese dioxide b. charcoal powder c. sulphur dioxide d. only (a) and (b) ANSWER: only (a) and (b) 16)   The handle of iron box is made up of  a. Bakelite b. Ebonite c. Chromium d. Only (a) and (b) ANSWER: Only (a) and (b) 17)   Heating element of electric iron box is an alloy of  a. Copper and nickel b. Nickel and cobalt c. Iron and magnesium d. Nickel and chromium ANSWER: Nickel and chromium 18)   Electric heaters is made up of  a. Chromed iron b. Brass c. Steel d. Both (a) and (b) ANSWER: Both (a) and (b) 19)   In telegraphic machine, the machine parts that sends the message and the machine parts that receives the message are  a. Morse key, Morse key b. Morse key, Morse sounder c. Morse sounder, Morse key d. Morse sounder, Morse sounder ANSWER: Morse key, Morse sounder 20)   Buzzer in principle is a bell  a. with hammer b. with gong c. with both hammer and gong d. without hammer and gong ANSWER: without hammer and gong https://t.me/ElectricalGuru

 RRB JE : BASIC ELECTRICAL ENGG. 1) Filters are used to convert  a. Pulsating dc signal into a pure dc signal b. Pure dc signal into a pulsating dc signal c. Pulsating dc signal into a pure ac signal d. Pulsating ac signal into a pure dc signal ANSWER: Pulsating dc signal into a pure dc signal 2)   The cut - in voltage for silicon and germanium are  a. 0.3 V, 0.3 V b. 0.3 V, 0.7 V c. 0.7 V, 0.7 V d. 0.7 V, 0.3 V ANSWER: 0.7 V, 0.3 V 3)   The P - type semiconductor impurities are also called as  a. Acceptor impurities b. Donor impurities c. Either (a) or (b) d. None of these ANSWER: Acceptor impurities 4)   In N - type semiconductor, the impurities added to a semiconductor are  a. Trivalent b. Pentavalent c. Monovalent d. Tetravalent ANSWER: Pentavalent 5)   Impurities are generally added in the pure semiconductor to  a. increase the number of electrons b. increase the number of holes c. increase their conductivity d. all of these ANSWER: increase their conductivity 6)   If induction motor is direct switched-on then it will develop  a. 1.5 times their full load torque b. 1.5 to 2.5 times their full load torque c. 2.5 times their full load torque d. 1.5 to 5 times their full load torque ANSWER: 1.5 to 2.5 times their full load torque 7)   In DOL fuses are provided to protect against a. Short circuit protection b. Over voltage c. Over current d. Over load ANSWER: Short circuit protection 8)   In four - point starter, the no volt release is connected across the  a. Supply line through a protective resistance b. In series with field circuit through a protective resistance c. Either (a) or (b) d. None of these ANSWER: Supply line through a protective resistance 9)   The overload release protects the motor against  a. Over voltage b. Over current c. Over load d. All of these ANSWER: Over load 10)   3 - point starter is used to start the  a. Series motor b. Shunt motor c. Compound motor d. Only (b) and (c) ANSWER: Only (b) and (c) https://t.me/ElectricalGuru

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